BEAN FOOD

by
Dr. JOE SCHWARCZ

Dr. Joe Schwarcz is Director of McGill University’s Office for Science and Society. He hosts The Dr. Joe Show on Montreal's CJAD and has appeared hundreds of times on The Discovery Channel, CTV, CBC, TV Ontario and Global Television. Dr. Schwarcz also writes a newspaper column entitled The Right Chemistry and has authored four best sellers, Radar, Hula Hoops and Playful Pigs, The Genie in the Bottle, That's the Way the Cookie Crumbles, and Dr. Joe and What You Didn’t Know.

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Beans. They can cause gas. And we don’t need to carry out studies to prove it. But beans can also reduce the risk of heart disease and cancer. That claim, however, does require backing from scientific studies. Ideally, we would like to see an “intervention study,” in which subjects are organized into two groups with virtually identical lifestyles except for one aspect of the diet. The experimental group, but not the control group, would be treated to a prescribed dose of beans. Both groups would then have to be followed for many years. I suspect following the “bean” group would not be a tough task. Unfortunately, such intervention studies are very difficult to carry out and researchers are more likely to go for “case-control” trials.

In such a trial, a set of patients suffering from a certain disease is compared with a roughly equal number of healthy people, matched for age, lifestyle, place of residence, physical activity level, smoking, body weight and socioeconomic status. This is just what researchers at Harvard University did to try and tease out factors responsible for heart attacks in 2,118 individuals in Costa Rica. Much to their surprise, they found that eating a third of a cup of beans a day reduced the likelihood of suffering a heart attack by close to 40%! Just what in the beans is responsible isn’t clear, but beans are rich in folic acid, magnesium, vitamin B6, alpha-linolenic acid and fiber, each of which in theory can have an effect on heart function.

“Population studies” are another way to gain insight into causes of disease. The health status of a large number of initially healthy subjects is continuously monitored, as is their lifestyle. Subjects periodically fill out food frequency questionnaires, which are then analyzed in terms of specific dietary components. One of the best examples is the Nurses Health Study, which has followed over 90,000 nurses for many years, some of whom, as would be expected, developed breast cancer. Researchers theorized that the disease might be linked to a reduced intake of flavonols, compounds that due to their antioxidant potential are believed to protect against cancer. They therefore investigated the amounts of tea, onions, apples, broccoli, green pepper and blueberries, all rich in flavonols, in the nurses’ diet. The results were unexpected. There was no association between the total flavonol intake and breast cancer. But women who consumed beans or lentils twice a week were about 25% less likely to develop breast cancer than women who consumed them less than once a month. Just another example of how health effects are determined by the overall composition of a food, not by individual components.

Laboratory experiments and animal studies also offer clues about preventing and fighting disease. It may be these that will eventually shed light on why beans have anti-cancer properties. The secret just may lie in inositol pentakisphosphate, a substance found in beans, as well as in lentils, peas, wheat bran and nuts. Tumour growth involves many chemical reactions and specific enzymes play a major role in these. Phosphoinositide 3-kinases, first discovered in the 1980s, are involved in the development of lung, ovarian and breast cancer. Substances that block the activity of these enzymes are therefore obvious targets of research. Most compounds that have shown efficacy have turned out to be too toxic for use, but researchers at University College in London have great hopes for inositol pentakisphosphate which they have isolated from beans. This compound is remarkably non-toxic even in large amounts. In laboratory studies on human cells, the compound inhibited angiogenesis, the process tumours use to grow the blood vessels they need to supply them with nourishment. But even more interesting results were found when human ovarian cancer cells were transplanted into mice. Inositol pentakisphosphate had an effect comparable to that of cisplatin, the drug commonly used for ovarian cancer treatment. A further exciting finding was that this compound enhanced the effect of anti-cancer drugs!

In spite of the positive health effects of beans, people worry about including them in the diet. The fear of course is the potentially embarrassing emission of gases. Beans contain specific carbohydrates such as raffinose and stachyose, which are not broken down by our digestive enzymes in the small intestine. They therefore proceed to the colon where they delight the resident bacteria which proceed to gobble them up. Unfortunately for us, these bacteria produce a number of gases as they dine on these carbohydrates, some of which, like hydrogen sulphide, are notoriously odiferous. But science may come to our rescue here. Marisela Granito and colleagues at Simon Bolivar University in Venezuela have been investigating this issue for years, and have now found that fermenting beans with two specific bacteria of the Lactobacillus species before cooking can lower the concentration of the offending carbohydrates by 90% without altering the nutritional value of the beans. They propose that the food industry can make use of these bacteria to market low-gas beans. Scientists in India have taken another approach. Using standard food irradiation technology, they exposed beans to gamma rays and found that in combination with soaking, most of the stachyose and raffinose were eliminated.

Individuals react quite differently to beans in terms of gas production. Some can ingest copious amounts without a problem, others drive friends and family away after eating a single burrito. But even in the latter case, emissions can be decreased by slowly increasing bean intake. And in light of everything we know about the benefits of eating beans, it is worth making the effort. Replacing some of the meat in our diet with beans is a good idea. Maybe in that classic fairy tale, Jack didn’t do such a bad thing when he traded the family cow for the beans that grew into a giant beanstalk. .